I've lost count now of the number of times I've watched this demo and it still impresses me. It's been a great challenge to find all the secrets of the c128 this demo uses and I think I have finally found and implemented them all into my emulator! There is one minor glitch I need to fix in the Boris Vallejo image in the VIC version but everything else seems to run like a real c128. You can download and see for yourself here ==> http://www.z64k.com :)

To get a correct timing you need to measure the speed of the CPU relative to the speed of the VDC. In the beginning the demo measures the CPU cycles wasted for 64 frames. This number is then used to calculate the exact number of cycles per rasterline (i.e. 63.054 cycles per rasterline) and this again is then used to set timers or correct rasterroutine timing. For example, the rasterbars and techtech routine use a 63 cycle routine which on some rasterlines uses 64 cycles based on that 63.0xx clock cycles previously measured.

The new colors work because of the PAL color encoding: The color carrier consists of U (blue-yellow color distance) and V (red-cyan color distance) which are simply added together, so C = U + V. Now, because a decoder needs to seperate U and V again, the inventors of PAL used a simple trick: They inverted the sign of V every 2nd rasterline, so you always have C = U + V followed by C = U - V. This way you can simply take the color carrier of the previous rasterline and add or subtract the current rasterline with it. If you add both carriers you get back U, and if you subtract you get V or -V. Now, if you skip an odd number of rasterlines, you get -V where normally would be +V and you get +V where normally would be -V. -> The red-cyan color distance gets inverted.

Amidog: Frankly, we don't quite know ourselves! ;-) Crossbow was experimenting with that $d030-bit that almost all of the effects in the demo are based on and he noticed the colors came out different under certain conditions, because that bit forces an early restart of the screen and seriously fucks with the video signal. It does not work on every monitor we've noticed, some (Philips?) show the original colors!
From looking at the colors I would say that the green and the red component of the video signal got switched somehow. It's probably not YUV, but YVU (or GRB instead of RGB!).
Knowing what the colors looked like falsified i drew the gfx in Amicapaint and xbow made me a displayer so i could check what it looked like in false colors! ;-)
If you look closely you can see those colors in another part in the demo: The Border-IFLI-GFX. It's in the line xbow does the $d030-trick, we couldn't get rid of it so xbow managed to blend it in nicely! ;-) He also couldn't get rid of the white "pixel" (?) (that's from the horizontal clamp, the white line at the very left of the screen! adjust your monitor to show the very left and you'll see what i mean!), so he drew the "Boris Vallejo"-Logo and integrated the clamp-pixel into it, so noone would notice! ;-D

I am so happy I have a c128 with a c1901 monitor. This demo is simply amazing! And my c128 loves it too. The first time i ran the demo, it was like my c128 went -"Ahhh.. FINALLY! after all those years. Graham, u da man." (/:

User CommentSubmitted by Necronomfive on 22 August 2006

Excellent demo! The screenshot really sucks, and does this masterpiece aboslutely no justice. Both VDC and VIC parts are very colourful and great to watch. It took me a little while to figure out how they managed to get 13 new colours out of the VIC without mixing...

Of course everybody's taste is different, but there are also facts. And it's a fact that Risen from Oblivion is good, that's not a matter of taste. Can't understand how someone can give it a vote of only 2.

Edited 21st of May, 2010:
Hey it seems 8 years later the vote of only 2 points disappeared. Either someone made up his mind, or some user was removed from CSDb. :)

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